High power high frequency generators such as magnetrons operating in a pulse mode characteristically produce a wide spectrum of frequencies extending beyond the desired frequency range to be used. Such frequencies, having been previously absorbed by resistive loads, reflected back into the magnetron with deleterious results such as overheating of the cathode or in radar have been radiated into the atmosphere where they interfere with other equipment. Systems for absorbing such undesired frequencies have been very expensive when high power sources are involved and have been difficult to align and/or realign when a high frequency source has shifted slightly in frequency as, for example, when a magnetron burns out and is replaced in an existing equipment. While frequency responsive systems for coupling two or more widely separated frequencies to the same antenna have been used, such coupling systems did not filter frequency components closely adjacent the desired frequency band from the system. Alternative methods of treatment of the problem, such as generating signals at low power, filtering the desired frequency components from the generated signals and then amplifying the resultant filtered signals, are expensive and require complex tuning and/or retuning procedures.
In addition, if filtering is done by resonant techniques at high power, voltage nodes in the resonant system require extremely high voltage insulation for the radiated field, and such insulation is bulky, expensive and difficult to align.